要 旨 ：
Recent advances in nanoscience have demonstrated that
fundamentally new physical phenomena are found, when systems are reduced
in size to dimensions that become comparable to the fundamental
microscopic length scales of a material under study. Superconductivity
is a macroscopic quantum phenomenon, and therefore it is of particular
interest to see how this quantum state is influenced when the samples
are reduced to nanometer sizes. Nowadays, developments in
nanotechnologies and measurement techniques allow the experimental
investigation of the magnetic and thermodynamic superconducting
properties of mesoscopic samples in this regime. In this lecture, we
will present theoretical models to describe such nanoscale
superconducting systems and discuss possible new experimental phenomena
we can predict within these theoretical models.
We will consider the theory of interactions between two nanoscale ferromagnetic
particles embedded in a superconductor. In the London limit
approximation, we show that the interactions between ferromagnetic
particles can lead to either parallel or antiparallel spin alignment.
The crossover between those is dependent on the ratio of the
interparticle spacing and the London penetration depth. We will show
that a phase transition between spin orientations can occur as the
temperature is varied. Finally, we comment on the extension of these
results to arrays of nanoparticles in different geometries.
In view of modern experimental data, we consider also composite nanowires
made from both superconducting and ferromagnetic metals in the case of
cylindrical geometry, where one metal forms the core of a nanowire, and
the second forms an outer cylindrical sheath. Moreover, we analyze also
the inverse situation, in which a normal or ferromagnetic core is
surrounded by a superconducting sheath. In this case, it is interesting
to examine the spectrum of Andreev bound states in the normal or
ferromagnetic core.